Nowadays, mobile terminals such as smart phones are favored by more and more consumers. However, the mobile terminal consumes large power energy, and needs to be charged frequently.
Typically, the mobile terminal is charged by a power adapter. The power adapter generally includes a primary rectifier circuit, a primary filter circuit, a transformer, a secondary rectifier circuit, a secondary filter circuit and a control circuit, such that the power adapter converts the input alternating current of 220V into a stable and low voltage direct current (for example, 5V) suitable for requirements of the mobile terminal, and provides the direct current to a power management device and a battery of the mobile terminal, thereby realizing charging the mobile terminal.
However, with the increasing of the power of the power adapter, for example, from 5 W to larger power such as 10 W, 15 W, 25 W, it needs more electronic elements capable of bearing large power and realizing better control for adaptation, which not only increases a size of the power adapter, but also increases a production cost and manufacture difficulty of the power adapter.
Furthermore, when the power adapter is working, if a switching-mode power supply in the power adapter applies a non-secondary feedback, a magnitude of the output voltage mainly depends on a load, and it is hard to control the output precisely. However, if the switching-mode power supply in the power adapter applies a secondary feedback control strategy in the related arts, although a voltage waveform with a stable magnitude is output, an acquired power factor is not ideal, which limits an application range.